M-Indolocarbazole Derivative as a Universal Host Material for RGB and White Phosphorescent OLEDs

Abstract

The host materials designed for highly efficient white phosphorescent organic light-emitting diodes (PhOLEDs) with power efficiency (PE) >50 lm W -1 and low efficiency roll-off are very rare. In this work, three new indolocarbazole-based materials (ICDP, 4ICPPy, and 4ICDPy) are presented composed of 6,7-dimethylindolo[3,2-a]carbazole and phenyl or 4-pyridyl group for hosting blue, green, and red phosphors. Among this three host materials, 4ICDPy-based devices reveal the best electroluminescent performance with maximum external quantum efficiencies (EQEs) of 22.1%, 27.0%, and 25.3% for blue (FIrpic), green (fac-Ir(ppy) 3), and red ((piq) 2 Ir(acac)) PhOLEDs. A two-color and single-emitting-layer white organic light-emitting diode hosted by 4ICDPy with FIrpic and Ir(pq) 3 as dopants achieves high EQE of 20.3% and PE of 50.9 lm W -1 with good color stability; this performance is among the best for a single-emitting-layer white PhOLEDs. All 4ICDPy-based devices show low efficiency roll-off probably due to the excellent balanced carrier transport arisen from the bipolar character of 4ICDPy. Three new indolocarbazole-based host materials, ICDP, 4ICPPy, and 4ICDPy, are synthesized and used as hosts for various color phosphorescent organic light-emitting diodes. The blue, green, and red devices using 4ICDPy as the host all exhibit very high device efficiencies. In addition, a two-color white device shows an external quantum efficiency of 20.3% and power efficiency of 50.9 lm W -1 with excellent color stability.